In the case of using a pneumatic tire under heavy load and highly flexural conditions of up to 25 to 40% of a sectional height of the tire, when the tire is pressurized or travels on roads, an interlayer strain is produced between a bead core and its surrounding member and becomes excessively large. Particularly, when the tire travels on roads, such excessively large interlayer strain together with accumulation of heat tends to induce a separation between a metal cord of the rubberized bead core and its coating rubber on the one hand and between a rubberized fabric covering the bead core and its coating rubber on the other hand. This separation induces a separation failure of the bond between a portion of the metal cord of the rubberized bead core and its coating rubber and the portion of the metal cord of the rubberized bead core becomes free from its coating rubber, thereby inducing a breakage of the tire.
The invention will now be described in greater detail with reference to the accompanying drawings.